In A Day and a Night and a Day, Glen Duncan has set out to write a political thriller themed around "extraordinary rendition" and the Bush administration's use of torture. He's also interested in using the confrontation between interrogator and victim to stage a discussion of such topics as cultural malaise, the meaning of Islamist terrorism, and the difficulty of justifying moral commitments in a world lacking transcendent certainties. Political indignation, thriller motifs and post-religious anguish have informed some fine novels: Robert Stone's A Flag for Sunrise, for example. But instead of Stone or Dostoevsky or even Graham Greene, Duncan writes under the influence of Don DeLillo and Martin Amis in his post-1980s incarnation.

Augustus Rose, his central character, is first encountered coming to in a cell at a "black site" in Morocco, having been kidnapped in Barcelona, in about 2006. Interrogation and torture quickly follow under the supervision of a US operative named Harper, a wearer of Gap casuals who offers smokes between beatings. Another strand of the novel details Augustus's biography. He turns out to be a US citizen in his 50s, the son of an Italian-American mother and African-American father. Shaped by Catholicism and poverty in his childhood, and later by a love affair with Selina, a white fellow student in 60s New York, he has since built up an unusual CV. The third strand of the narrative finds him leading a solitary life on a remote Scottish island, a broken man thanks to his experience of the torture chamber. Waiting only for death, but still packing a handgun for self-defence, he meets a girl at a bus stop who ends up taking shelter in his rented croft.

As Duncan switches between these storylines, two of which are rendered in the present tense, the reasons for Harper's interest in Augustus are revealed with suspense-sapping speed.It turns out that Augustus - who has worked as a foreign correspondent and, more recently, a restaurateur - has spent the last two years infiltrating an Islamist cell that once bombed a department store in Barcelona. He's done this on behalf of a shadowy group that tries to take bad guys off the world stage, a kind of armed NGO, with western politicians as well as developing-world tyrants and terrorists on its hit list. This group has recently tried to assassinate George Bush, thereby making itself a priority for Harper's bosses.As for the question of what's prompted Augustus to leave the restaurant business for vigilante spy work, we learn early on that he had a short-lived reunion with Selina in Barcelona, and that he signed up as an infiltrator soon after the department-store bombing.

Thriller conventions license improbable scenarios, but Duncan lays out Augustus's story without helping the reader suspend much disbelief. Large chunks of the hero's life are told in fast-forward, sometimes because of plausibility worries - we're told next to nothing about Augustus's training and time spent posing as an Islamist militant - and sometimes out of exhausted contempt for the kind of writing that seems to be called for. "He was the protagonist in a million creative writing class short stories, one more quiet sufferer lost in the American dream": a quick page of such lines takes Augustus through two decades. The book's central implausibility, however, concerns Harper, who's a mouthpiece for low-rent cultural theorising as well as a spokesman for nihilistic cynicism. Instead of a vengeful sadist or a nervous careerist, he's a garrulous student of postmodernity, forever breaking off the torture session to chat about Baudrillard or reality TV in the style of an escapee from DeLillo's White Noise.

Duncan, the British author of six previous novels (including I, Lucifer and The Bloodstone Papers), does a fairly good job of giving his characters American vocabularies. His writing aims for hardboiled terseness mixed with figurative density, sometimes leading to extravagant word-choices ("the crenulations of his brain"; "our thanatotic glands are juicing"). He often leaves out indefinite articles ("a bony white girl with small face"; "an American with jewelish green eye") or uses words in unconventional forms (Selina has "long legs and natural blond"). As a result, his poeticisms - "The fit of a gun's grip in your hand is of the deep geometry", for example - are sometimes hard to disentangle from the copy-editing errors. Sabrina Harman of Abu Ghraib fame appears as "Sabrina Harmon". Augustus tries to picture what someone else is "going though". At one point we're told that Selina's bedroom is "too hot to cover even with a sheet"; an editor should have fixed this, along with the dangling modifier on the first page.

The depressing thing about these problems is that Duncan isn't a hack writer. His characters' musings on the meaning of life have the ring of heroic sincerity, and even the sentences that don't mean what they ought to have been put together with great care for stylistic effects. On a larger scale, he seems to have persuaded himself that hackneyed plot manoeuvres can be justified by making the characters' sensitivity to the hackneyed a subject of debate in the novel. He comes across as a writer who's become so absorbed by sentence rhythms on the one hand and grand themes on the other that he's lost all perspective on his performance as a whole.

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